A 3rd Generation Partnership Project (3GPP) wireless core network comprises a General Packet Radio Service (GPRS) network, an Evolved Packet System (EPS) network, and a Universal Mobile Telecommunications System (UMTS).
FIG. 1 shows a schematic diagram of an emergency call performed by a piece of MTC User Equipment (UE) to access an Internet Protocol (IP) Multimedia Subsystem (IMS) through System Architecture Evolution (SAE) and a UMTS. In FIG. 1, the solid lines represent signalings, and the dashed lines represent IP channels of the subscriber. When the access is performed through the UMTS, the UE can be also called a Mobile Station (MS).
As shown in FIG. 1, main network elements involved when the MTC UE accesses an MTC server through an EPS or a UMTS comprise: network elements of an EPS network, network elements of a UMTS network and the MTC server. In this case, the MTC UE can be also called an MTC device.
Since a 3GPP Release 7 standard system is established, a policy and charging function is realized by a Policy and Charging Control (PCC) framework. The PCC architecture is a functional framework which can be applied to various access technologies, e.g. the PCC framework can be applied to a UMTS, a Global System for Mobile Communications (GSM) an Enhanced Data rates for GSM Evolution (EDGE) radio access network, an Internetworking Wireless Local Area Network (I-WLAN) and an EPS.
PCC mainly realizes two major functions of policy control and charging. FIG. 2 is a schematic diagram illustrating an existing, PCC composition architecture. Each logical function entity and interface functions thereof in the PCC architecture as shown in FIG. 2 are described below.
Application Function (AF) is an access point for providing service applications. Dynamic policy control needs to be applied to network resources used by these service applications. When parameter negotiation is performed at a service plane, the AF delivers related service information to a Policy and Charging Rules Function (PCRF). If the service information is consistent with a policy of the PCRF, the PCRF accepts the negotiation; otherwise, the PCRF refuses the negotiation and provides PCRF-acceptable service parameters during a feedback process. Subsequently, the AF can return these parameters to a UE, wherein an interface between the AF and the PCRF is an Rx interface.
The PCRF is the core of the PCC and is configured to decide policies and establish charging rules. The PCRF provides a network control rule based on a service data flow, wherein the network control comprises detection of service data flows, gating control, control of Quality of Service (QoS) and data flow-base charging rules etc. The PCRF sends policies and charging rules established by the PCRF itself to a Policy and Control Enforcement Function (PCEF) to be enforced. At the same time, the PCRF further needs to ensure the consistency between these rules and subscription information of subscribers, wherein the basis for the PCRF to establish the policies and the charging rules comprises: service-related information obtained from the AF, subscriber policy and charging control subscription information which is related to policy control and charging and is obtained from a Subscription Profile Repository (SPR), and bearer-related network information obtained from the PCEF via a Gx interface.
The PCEF, usually located in a Gateway (GW), is configured to enforce, at a bearing plane, the policies and the charging rules established by the PCRF. The PCEF detects the service data flows according to a service data flow filter in the rules sent by the PCRF, and further enforces the policies and the charging rules established by the PCRF on these service data flows. When a bearer is established, the PCEF performs resource distribution according to the rules sent by the PCRF and performs gating control according to information provided by the AF. At the same time, the PCEF reports an event happening on a bearer network according to trigger of an event subscribed by the PCRF. According to the charging rules sent by the PCRF, the PCEF enforces corresponding charging operation of the service data flows, wherein the charging may be either online charging or offline charging. If it is online charging, the PCEF needs to perform credit management together with an Online Charging System (OCS). If it is offline charging, relevant charging information is exchanged between the PCEF and an Offline Charging System (OFCS). An interface between the PCEF and the PCRF is a Gx interface, an interface between the PCEF and the OCS is a Gy interface, and an interface between the PCEF and the OFCS is a Gz interface. The PCEF is generally located in a network gateway, such as an EPS Packet Data Network GW (PDN-GW), a GPRS Gateway Support Node (GGSN) in a GPRS and a Packet Data Gateway (PDG) in an I-WLAN.
A Bearer Binding and Event Reporting Function (BBERF) is generally located in an Access Network Gateway (ANG). For example, when a UE accesses an EPS through an E-UTRAN and Proxy Mobile Internet Protocol version 6 (PMIPv6) is used between a Serving Gateway (S-GW) and a Packet Data Network Gateway (P-GW), the BBERF is located in the S-GW; when the UE accesses through a trusted non-3GPP access network, the BBERF is located in a trusted non-3GPP access gateway.
The SPR stores the subscriber policy and charging control subscription information related to the policy control and charging. An interface between the SPR and the PCRF is a Sp interface.
The OCS and the PCEF together control and manage the subscriber credit under an online charging mode.
The UFCS and the PCEF together implement charging operation under an offline charging mode.
In existing techniques, an MTC device (i.e. a terminal) needs to establish an Internet Protocol-Connectivity Access Network (IP-CAN) session through an EPS or an UMTS first before accessing an MTC server. In order to realize policy and charging control for the IP-CAN session, a policy enforcement function in the EPS or the UMTS system establishes a Diameter session for each IP-CAN session with the PCRF. Through the Diameter session, the policy enforcement function reports access information of the MTC device to the PCRF, and the PCRF delivers a policy to the policy enforcement function.
The inventors found that daring practical application, there are a large number of MTC devices which need to be online for a long time; if the PCRF needs to apply for a policy applied to an IP-CAN session during an establishment process of the IP-CAN session of each MTC device, a lot of network resources will be occupied to reduce the utilization of the network resources, thus resulting in waste of the network resources.